1. Field of the Invention
The present invention relates to a method for charging a communication fee in a GSM (Global System for Mobile communication)/UMTS (Universal Mobile Telecommunication System) mobile communication system, and more particularly to a method for performing communication using a collect call.
2. Description of the Related Art
Generally, mobile stations in a GSM/UMTS-based mobile communication system include Subscriber Identity Module (SIM) cards or Universal Subscriber Identity Modules (USIM) cards in the inner or outer parts thereof. These SIM/USIM cards including user information, user authentication, and roaming information are essential under the GSM/UTMS environment.
Accordingly, a user may freely use a communication service by obtaining a mobile communication terminal only if the user carries a SIM/USIM card issued by the communication service provider.
The SIM/USIM cards include a function of enabling a prepaid service in which predetermined sums desired by a user are previously charged and used. In other words, through the prepaid SIM card, a user prepays predetermined sums of money for a communication fee and charges the predetermined sums, thereby being able to make calls during a time period corresponding to the charged sums.
FIG. 1 is a flowchart illustrating a typical communication procedure according to a call request of a mobile station.
Referring to FIG. 1, a mobile station 102 transmits a setup message to a GSM/UMTS-based network 104 in order to request a call to a specific mobile station 106 (step 108). The network 104 transmits the setup message to the corresponding mobile station 106 so as to inform the mobile station 106 of the fact that the mobile station 102 has requested a call (step 110). After receiving the setup message, the mobile station 106 transmits to the network 104 a call confirmed message indicating that the mobile station 106 has recognized the request of the call by the mobile station 102 (step 112). The network 104 receives the call confirmed message so as to transmit a “call processing” message to the mobile station 102 (step 114). The mobile station 106 transmits an alerting message to the network 104 so as to report that a call will be connected (step 116). The network 104 delivers the alerting message to the mobile station 102 (step 118).
The call connection is established between the mobile station 102 having requested the call and the mobile station 106 having confirmed the call request (steps 120 and 122), and the mobile station 102 transmits a “connect ack” message to the mobile station 106 (steps 124 and 126), thereby completing the call connection procedure between the mobile stations 102 and 106.
Herein, if there are no sums charged in a prepaid SIM/USIM card of the mobile station 102 requesting a call, the mobile station 102 cannot transmit the setup message to the network 104. In other words, the conventional mobile station 102 cannot originate a call if there are no sums charged in the prepaid SIM/USIM card. In addition, the conventional mobile station 102 cannot even use a short message service (SMS).